Guardiola angrily confronted the referee Lee Mason after the game, claiming that the tackle was worthy of a red card rather than a booking, and said his "artists" needed more protection.
Aguero has been linked with moves away from the Etihad since the arrival of Pep Guardiola but finished last season with more than 20 Premier League goals for a fourth successive campaign.
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Kevin de Bruyne, Eliaquim Mangala, Danilo and Claudio Bravo remain out.
"He is injured. I don't know (how long he'll be out)".
City announced on Friday that the club's all-time leading goalscorer Aguero agreed to add another year to his deal, tying him to the club until June 2021. "Cardiff has a way to play and we have to adapt".
Manchester police said they had opened a hate crime investigation into the incident. "You have to be able to handle it. He's one of the players who shows his commitment to the club every day".
The Frenchman has missed the past two games and has been ruled out for an indefinite period with a bruised metatarsal. There are a lot of players, that have got things to improve and learn, but being in this Club you learn and improve faster than anywhere else. "Everybody can improve", Guardiola told a news conference ahead of Saturday's game at Cardiff City.
"Hopefully I can be back soon, help the team, and perform well. I know Liverpool and Chelsea are good, I still think this is the team that have got everything in their locker so it is a real test for you as a team and staff".